Bridles for Stability of a Powered Kite and a System and Method for Use of Same

ABSTRACT

The system may include a ground station, a tether attached to a ground station on a first end and to two or more bridles on a second, and a kite. The kite may include a main wing. Each bridle of the two or more bridles may be attached to the main wing, and the two or more bridles may be adapted to provide a torque on the kite to control a roll of the kite.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 13/070,157, filed Mar. 23, 2011, which claimspriority to U.S. Provisional Application No. 61/341,029, filed Mar. 24,2010. The entire contents of U.S. patent application Ser. No. 13/070,157and U.S. Provisional Application No. 61/341,029 are herein incorporatedby reference into the present application.

BACKGROUND

Embodiments disclosed herein relate to airborne flight and powergeneration systems, and more specifically to an airborne vehicleconfigured to maintain pitch control during tethered take-off andlanding.

SUMMARY

The present disclosure discloses embodiments that relate to bridles forstability of a powered kite.

In one aspect, a system is disclosed. The system may include a groundstation, a tether attached to the ground station on a first end and totwo or more bridles on a second end, and a kite. The kite comprises amain wing. Each bridle of the two or more bridles is attached to themain wing, and the two or more bridles are adapted to provide a torqueon the kite to control a roll of the kite.

In another aspect, a method is disclosed. The method may involve causinga kite to lift off the ground in a hover mode of flight. The kitecomprises a main wing. The kite is oriented vertically in the hover modeof flight. The method may involve controlling a roll of the kite duringthe hover mode of flight at least in part with use of two or morebridles between the kite and a tether. Each bridle of the two or morebridles is attached to the main wing, and the two or more bridles areadapted to provide a torque on the kite to control the roll of the kite.

In another aspect, a method is disclosed. The method may involve causinga kite to lift off the ground in a hover mode of flight. The kitecomprises a main wing. The kite is oriented vertically in the hover modeof flight. The method may involve transitioning the kite from the hovermode of flight to a crosswind mode of flight. The kite is orientedhorizontally in the crosswind mode of flight. And the method may involvecontrolling a roll of the kite during the crosswind mode of flight atleast in part with use of two or more bridles between the kite and atether. Each bridle of the two or more bridles is attached to the mainwing, and the two or more bridles are adapted to provide a torque on thekite to control the roll of the kite.

In another aspect, a system is disclosed. The system may include meansfor causing a kite to lift off the ground in a hover mode of flight, andmeans for controlling a roll of the kite during the hover mode of flightat least in part with use of two or more bridles between the kite and atether. The kite comprises a main wing. The kite is oriented verticallyin the hover mode of flight. Each bridle of the two or more bridles isattached to the main wing, and the two or more bridles are adapted toprovide a torque on the kite to control the roll of the kite.

In yet another aspect, a system is disclosed. The system may includemeans for causing a kite to lift off the ground in a hover mode offlight, means for transitioning the kite from the hover mode of flightto a crosswind mode of flight, and controlling a roll of the kite duringthe crosswind mode of flight at least in part with use of two or morebridles between the kite and a tether. The kite comprises a main wing.The kite is oriented vertically in the hover mode of flight. The kite isoriented horizontally in the crosswind mode of flight. Each bridle ofthe two or more bridles is attached to the main wing, and the two ormore bridles are adapted to provide a torque on the kite to control theroll of the kite.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are disclosed in thefollowing detailed description and the accompanying drawings.

FIG. 1 is a diagram illustrating an embodiment of a tethered kite systemaccording to some embodiments of the present disclosure.

FIG. 2 is a diagram illustrating a powered kite system in hover modeaccording to some embodiments of the present disclosure.

FIG. 3A is a sketch of a powered kite according to some embodiments ofthe present disclosure.

FIG. 3B is a sketch of a powered kite according to some embodiments ofthe present disclosure.

FIG. 4 is a diagram illustrating powered kite in crosswind flight, andassociated coordinate system and apparent wind vector, according to someembodiments of the present disclosure.

FIG. 5A is a diagram of a powered kite showing a first orientation ofthe tail wing according to some embodiments of the present disclosure.

FIG. 5B is a diagram of a powered kite showing a second orientation ofthe tail wing according to some embodiments of the present disclosure.

FIG. 5C is a diagram of kite and tail wing geometry according to someembodiments of the present disclosure.

FIG. 5D is a diagram of various kite and tail wing positions accordingto some embodiments of the present disclosure.

FIG. 5E is a diagram of a kite in hover mode with a pitch orientationaccording to some embodiments of the present disclosure.

FIG. 6A is a drawing of a kite according to some embodiments of thepresent disclosure.

FIG. 6B is another drawing of a kite according to some embodiments ofthe present disclosure.

FIG. 7 is a sketch of a kite mounted on a take-off structure accordingto some embodiments of the present disclosure.

FIG. 8 is a drawing of a kite according to some embodiments of thepresent disclosure.

FIG. 9 is a flow chart of a method according to some embodiments of thepresent disclosure.

FIG. 10 is a flow chart of another method according to some embodimentsof the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure can be implemented in numerousways, including as a process; an apparatus; and a system. In thisspecification, these implementations, or any other form that theembodiments may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the disclosure. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the presentdisclosure is provided below along with accompanying figures thatillustrate the principles of the embodiments. Numerous specific detailsare set forth in the following description in order to provide athorough understanding of the embodiments of the present disclosure.These details are provided for the purpose of example. For the purposeof clarity, technical material that is known in the technical fieldsrelated to the embodiments has not been described in detail so that thedisclosure is not unnecessarily obscured.

A configuration of aerodynamic surfaces and actuators useful in thelaunch, hover, transition, and landing of a powered kite is disclosed.In some embodiments, the powered kite comprises a main wing, a tailwing, and may comprise a number of other wings. The kite is connected toa tether which is connected to the ground or some other object. The kitecomprises a number of rotors, which are used to generate thrust with theinput of power or generate power at the cost of drag. The tail wing ofthe powered kite is located behind and above the center of mass andtether attachment location on the powered kite in the aerodynamic frameof the crosswind or static modes of flight. The tail wing is partiallyor fully actuated such that the tail wing maintains primarily attachedaerodynamic flow and augments the stability of the kite when the kite istransitioning to and from the hovering mode of flight and while the wingis in the hovering mode of flight. The placement and actuation of thetail foil in the manner described improves the aerodynamic stability andincreases the aerodynamic control authority in some modes of flight overa range of environmental conditions including conditions associated witha range of wind magnitudes, a range of wind directions, and a range ofother qualities of wind.

A powered kite which is flown both in the manner of a tethered aircraftand in the manner of a tethered helicopter can be designed toincorporate aerodynamic surfaces that improve the pitch-axis aerodynamicstability of the craft in both modes of flight while having nosignificant detrimental effects on the stability in other axes. Whenflying in the manner of an aircraft on a string, the kite must primarilycontrol or passively attenuate tension on the tether through the pitchaxis of the kite in order to increase fatigue life or decrease tetherand wing structural size and mass. When hovering in the manner of ahelicopter, the kite must have adequate control authority on the pitchaxis to prevent uncontrollable excitation of the tether by gusts ofwind. Control of the pitch axis in both modes of flight may be improvedby an all-moving tail high above and behind the main wing. When flyingas a tethered airplane, the tail wing acts in the manner of a normaltail. Additionally, in some embodiments, the tail may add a stabilizingeffect through tailoring of the tail wing airfoil drag coefficient suchthat it produces higher drag at negative angles of attack and lower dragat positive angles of attack, in a manner which increases the stabilityof the powered kite. When hovering, the apparent wind on the kite isroughly perpendicular to the main wing of the kite. When rotated 90degrees to the main wing such that it faces into the wind whilehovering, the tail wing provides a restoring moment. While it ispossible to build a powered kite without this particular configurationof the aerodynamic surfaces, such a kite necessarily requires faster andmore accurate control signals, and is thus less robust against sensornoise and component failure. While a tail on an aircraft can be placedin a similar location relative to the main wing for the purpose ofkeeping the horizontal tail out of the wake of the main wing, it doesnot serve the same purpose of canceling the aerodynamic moment abouteither or both the center of mass and tether attachment point when themain wing of the kite is either roughly parallel or roughlyperpendicular to the perceived wind. It additionally does not serve thepurpose of reducing excitation of the tether from wind while hovering.

In some embodiments of the present disclosure, as seen in FIG. 1 apowered kite 101 is adapted to fly while tethered. In some embodiments,the kite 101 comprises one or more airfoil elements with turbine drivengenerators mounted thereon. The kite 101 is attached by tether 102 toobject 103, which may be a ground unit. In some embodiments, the groundunit may include winding and/or winching elements adapted to extend orto reel out the tether. In some embodiments, the tether 102 comprisesboth structural and electrical conductive aspects. The ground unit maybe adapted to receive electrical energy routed from the kite 101 viatether 102. In some embodiments, kite 101 may operate in a crosswindmode of flight. Kite 101 may also fly in other modes of flight,including the stationary mode of flight and the hovering mode of flight.Kite 101 may be adapted to transition between the aforementioned modesof flight.

In some embodiments, kite 101 takes off from the ground in the hoveringmode of flight and transitions into the crosswind mode of flight, forthe purpose of electrical power generation. In some embodiments, theground unit may include aspects adapted to support the kite while on theground. In some embodiments, the kite is a positioned in a verticalconfiguration such that the “front” of the kite faces upward whileconstrained in the ground unit. In some embodiments, the system isadapted to begin a power generation mode with the kite constrained inthe ground unit in such a manner. The turbine driven generators may beadapted to also function as motor driven propellers. The kite may usethe motor driven propellers to provide thrust vertically downward inorder to take off from the ground and raise to a desired altitude. Asthe kite increases its altitude, the ground unit may extend the tether.In some embodiments, the tether tension is monitored during the take offportion of a flight of the kite. At a desired altitude, the kite maybegin a transition from the substantially vertical take-off mode to aregular flight mode, as described below. At the end of a flight, thekite 101 may transition out of a regular mode of flight into the hovermode of flight to land.

In some embodiments, after transitioning from hovering mode the kite 101may fly in a regular, stationary flight mode at the end of the tether102. In some embodiments, the kite 101 may fly in crosswind flightpatterns. In some embodiments, the crosswind flight pattern may besubstantially circular. In some embodiments, other flight patterns maybe flown. In the crosswind mode of flight, kite 101 may fly on aflightpath 104 at an inertial velocity of equal or greater order ofmagnitude to the wind velocity 105. In various embodiments, flightpath104 comprises a path through space, a path through a parameter spaceincluding prescribed targets through the path for power generation,tether tension, or other measurable variable, or any other appropriatepath. In various embodiments, parameters comprise one or more of thefollowing: tension on tether 102, load on kite 101, angular rotationrate of kite 101, or any other appropriate parameter.

In the stationary mode of flight, kite 101 may fly at a small inertialvelocity compared to wind velocity 105. In this mode of flight, themajority of the lift holding kite 101 aloft comes from the flow of wind105 over wings of kite 101.

When transitioning between modes of flight, kite 101 changes from onemode of flight to another mode of flight. In various embodiments, thetransition modes of flight comprise highly dynamic maneuvers, slowmaneuvers in nearly static balance, or any other appropriate maneuvers.

FIG. 2 is a diagram illustrating an embodiment of a powered kite in thehovering mode of flight. In some embodiments of the present disclosure,the hovering mode of flight kite 201 uses rotors or some other means ofon-board power to create thrust to oppose the force of gravity and tomaintain position or move to a target position. In some embodiments, theturbine driven generators used to generate electrical energy while incrosswind flight mode may also function as motor driven propellers whilein hover mode. Some force to oppose gravity may still be derived fromwings of kite 201. In this mode of flight, the apparent wind 214 may beroughly perpendicular to the orientation of kite 201. Object 203 may bea ground station which supplies power to rotors on kite 201 to generateon-board thrust. In some embodiments, power to the rotors is provided bya power source on kite 201.

In various embodiments, object 203 comprises a base station attached tothe ground, a ship, a cart, a payload not affixed to the ground, or anyother appropriate object to which tether 202 is attached. In someembodiments, object 203 supplies power to kite 201 when thrust is beingoutput by rotors on kite 201 and receives power from kite 201 whenrotors are generating power at the expense of drag. In some embodiments,kite 201 uses on-board power such as batteries or a gas engine toprovide power to rotors as needed.

Tether 202 comprises a high strength material to convey mechanical forcefrom kite 201 to object 203. Tether 202 includes an electrical elementto convey electrical power to kite 201 from object 203 or from object203 to kite 201. In some embodiments, the electrical and mechanicalelements of tether 202 are the same element. In some embodiments, tether202 comprises elements to convey other forms of energy. In variousembodiments, tether 202 comprises a fixed length tether, a variablelength tether, or has any other appropriate characteristic or propertyfor a tether. In some embodiments, tether 202 is able to be reeled in ona spool associated with object 203 or on a spool associated with kite201.

In some embodiments of the present disclosure, as seen in FIG. 3A a kiteis adapted to fly in the various flight modes discussed above. In someembodiments, the kite 301 of FIG. 3A is used to implement kite 101 inthe system of FIG. 1 or to implement kite 201 in the system of FIG. 2.In the example shown, kite 301 comprises a plurality ofturbine/propellers, hereafter rotors 310. The rotors 310 compriseaerodynamic surfaces connected to a means of actuation which are used togenerate power in the manner of a wind turbine, at the expense ofincreased drag, or are used to create thrust by the input of electricalor mechanical power. In some embodiments, the rotors 310 comprise anelectric motor/generator connected to a fixed or variable pitchpropeller. In various embodiments, a motor associated with a rotor ofrotors 310 comprises a gas motor, the aerodynamic surface comprises aflapping wing, or the rotor comprises any other actuated aerodynamicsurface capable of converting airflow into mechanical power ormechanical power into airflow. In some embodiments, rotors 310 are usedto extract power or apply thrust while kite 301 is flying in thecrosswind mode of flight along a flightpath, or in the static mode offlight, or is used to apply thrust when kite 301 is hovering (e.g., asdepicted in FIG. 5B). In some embodiments, rotors 310 are only capableof producing thrust. In various embodiments, rotors 310 comprise fourindividual rotors, a single individual rotor, or any other appropriatenumber of individual rotors or other aerodynamic actuators.

In the example shown, the kite 301 comprises a plurality of wings, forexample, two wings 311 and 312. The main wing 311 comprises the mainwing surface of the kite 301, and provides the majority of aerodynamicforce in some modes of flight. In some embodiments, the main wing 311comprises multiple wing sections. The tail wing 312 comprises therearward wing surface of kite 301, and provides a smaller aerodynamicforce primarily used to achieve stability and maintain a balance offorces and moments for the kite 301. In some embodiments, the tail wing312 comprises many wing sections. In various embodiments, the kite 301comprises other wings, such as wing 313, which are used for thegeneration of further lift, for further augmentation of the stability ofthe kite 301, to reduce the drag of some structural element of kite the301, or for some other appropriate purpose. In some aspects, the wings311, 312 and 313, and any other wings which the kite 301 comprises, androtors 310 are connected by structural supports (e.g., spars).

In various embodiments, main wing 311, tail wing 312, the wing 313, andother wing surfaces on the kite 301 comprise rigid single elementairfoils, flexible single element airfoils, airfoils with controlsurfaces, multiple element airfoils, or any other combination of airfoiltypes. In some embodiments, control surfaces on some wings on the kite301 are deflected in the hover mode of flight in order to modify theaerodynamic properties or change the stability properties of the kite301. In various embodiments, deflection of the trailing or leadingelement of a multi-element airfoil on a wing is used to induce stall forthe desired portion of the transitions between flight modes, to changethe center of aerodynamic pressure on that wing in the hovering mode offlight, or to stabilize the aerodynamic flow around the wing in a mannerwhich reduces load variability on the wing in the hovering mode offlight.

FIG. 3B is an illustrative example of a kite 350 according to someembodiments of the present disclosure. In this illustrative example, amain wing 352 provides the primary lift for the kite 350. The main wing352 may have a wingspan of 8 meters. The area of the main wing 352 maybe 4 square meters, and the main wing 352 may have an aspect ratio of15. Four rotors 351 that may each include a turbine driven generator aremounted to the main wing 352 using pylons 356. The vertical spacingbetween the rotors may be 0.9 meters, equally spaced above and below themain wing 352. The turbine driven generators are adapted to alsofunction as motor driven propellers in a powered flight mode, or inhover mode. The propeller radius may be 36 centimeters. A tail boom 354is used to attach the rearward control surfaces to the main wing 352,and by extension, to the tether. The length of the tail boom may be 2meters. A vertical stabilizer 355 is attached to the rear of the tailboom 354. Atop the vertical stabilizer 355 is the tail wing 353. Thetail wing 353 may be 1 meter above the center of mass of the kite 350.The tail wing surface area may be 0.45 square meters. The kite 350 maybe flown on a 140 meter tether in some embodiments.

Other configurations of the kite 350 are possible as well. For instance,in some embodiments, the tail wing 353 may be about 3.7 meters (or about2-5 meters) above the center of mass of the kite 350. Moreover, in someembodiments, the length of the tail boom may be 7 meters (or about 6-8meters). Further, in some embodiments, the main wing 352 may havewingspan of 26 meters (or about 20-30 meters). Further still, in someembodiments, the tail wing 353 may be located in front of verticalstabilizer 355. Moreover, in some embodiments, the kite 350 may weigharound 1 ton.

Moreover, in some embodiments, the tail wing 353 may not be locatedabove the main wing 352. Instead, in some embodiments, the tail wing 353may be located below the main wing 352 or at the same elevation as themain wing 352. Further, in some embodiments, a kite may not include atail wing.

Although illustrated herein with a single element airfoil, in someembodiments the airfoil may comprise a plurality of elements. In someembodiments, there may be stacked airfoils, or other airfoilconfigurations.

FIG. 4 is a diagram illustrating an embodiment of a kite. In the exampleshown, kite 401 is flying in either the crosswind or static modes orflight. Kite 401 flies into an apparent wind 414 equal to the vectoraddition of the inertial velocity of the kite to the inertial velocityof the wind. The locations of various elements comprising kite 401 isdenoted in coordinate frame 418. In coordinate frame 418, axis 416 onthe kite, antiparallel to apparent wind 414, is denoted as ‘x.’ ‘Z’-axis415 points opposite the direction of lift when kite 401 is flying in thecrosswind mode of flight. ‘Y’-axis 417 is perpendicular to both ‘x’ axis416 and ‘z’ axis 415 in a manner which gives a right-handed coordinatesystem when the coordinates are listed in the order [‘x,’ ‘y,’ ‘z’].

In various embodiments, tether 402 is attached to kite 401 at onelocation, at two locations (e.g., to one side of the wing and to theanother side of the wing or toward the front of the kite and toward theback of the kite), at a number of points on the kite (e.g., four) andwhere the tether is attached to a number of other bridles that attach tothe number of points, or any other number of appropriate locationseither directly or indirectly using bridles and/or any other appropriateconnectors. In various embodiments, tether 402 is attached rigidly at asingle point on kite 401 through all modes of flight, is attached in amanner that the center of rotation changes depending on the direction offorce from the tether or due to some other variable, or any otherappropriate manner of attachment. In various embodiments, the center ofrotation of tether 402 on kite 401 is controlled by a linkage, aconfiguration of ropes or cables or some other appropriate mechanism. Insome embodiments, tether 402 is affixed directly to kite 401. In someembodiments, tether 402 is attached to kite 401 in a manner such thatthe center of rotation tether 402 is different on different axes. Invarious embodiments, tether 402 is attached so that it can be releasedfrom kite 401, is permanently affixed, or is attached in any otherappropriate manner

In some embodiments, the raised aspect of the tail wing relative to themain wing, as viewed with the kite in a horizontal configuration, allowsfor an additional method of pitch control of the kite while the kite isin hover mode. With the kite facing vertically upward, the center of thelift of the tail wing resides rearward of the kite in a manner thatallows changes in lift of the tail wing to use the lever arm of therearward distance (the amount that the tail wing was above the main wingin the horizontal configuration) to put a moment around the center ofgravity of the hovering kite. This force generated with the change inlift, levered around the distance behind the center of mass of the kite,puts a torque into the system such that changes in pitch of the kite canbe controlled. As the kite may oscillate in pitch during maneuvers andhovering, a further rearward position (“raised position” in horizontalflight mode) of the tail wing during hover mode allows for some pitchingof the kite while still maintaining the rearward aspect relative tovertical from ground. In some embodiments, the kite may be expected topitch backward 10 degrees due to dynamic changes in wind, wind gusting,and for other reasons. In more extreme cases, 20 degrees of pitchvariation may be seen. With a 10 degree design margin designed in beyondthat, a design may be desired such that the center of lift of the tailwing is at a higher point than a 30 degree line rising rearward throughthe center of gravity of the kite, as viewed in a horizontalconfiguration. In some embodiments, the tail wing may be adapted torotate above a point on a line that is angled 20 to 30 degrees off ahorizontal axis through the center of mass, as viewed in a horizontalconfiguration. Although the kite will rotate about a center of rotationwhich includes the tether in its determination in most aspects oftethered flight, in hover mode the tether tension may vary, and thus thecenter of rotation in pitch may also vary between the center of mass ofthe kite and a location towards the tether.

FIGS. 5A and 5B are diagrams illustrating embodiments of a kite. In theexamples shown, the tail wing 512 is shown in two orientations relativeto the kite 501. Coordinate system 518 is assumed to be affixed to thekite 501. The tail wing 512 is located at a significant negativelocation on x axis 516 relative to both the attachment point of thetether 502 to the kite 501, or to the center of mass 520 of the kite501. The main wing 511 is located at a significant negative location onz axis 515 relative to both the attachment point of the tether 502 tothe kite 501, and to the center of mass 520 of the kite 501. Axis 517 isperpendicular to both x axis 516 and z axis 515. The tail wing 512 isfurther capable of being partially or fully rotated by means ofmechanical or aerodynamic actuation. FIG. 5A illustrates the tail wing512 positioned roughly parallel to the main wing 511 such that the tailwing 512 will maintain primarily attached aerodynamic flow in some orall of the range of conditions for which main wing 511 maintainsprimarily attached aerodynamic flow. In this orientation the tail wing512 augments the stability of kite 501 by providing an aerodynamicrestoring force in addition to an aerodynamic damping force. Theorientation as seen in FIG. 5A may be used in stationary or cross windflight in some aspects.

FIG. 5B illustrates the tail wing 512 positioned roughly perpendicularto the main wing 511 such that for apparent wind antiparallel to z axis515, the tail wing 512 will maintain attached aerodynamic flow andprovide both an aerodynamic restoring force and an aerodynamic dampingforce. The configuration as seen in FIG. 5B may be illustrative of thehover mode. The tail wing 512 may be actuated to provide desired controlforces or may be held fixed in each mode of flight. In variousembodiments, the tail wing 512 is rotated by means of a mechanicalactuator or by means of the movement of an aerodynamic control surface.In some embodiments, the tail wing 512 rotates about a fixed pointlocated within the airfoil. In various embodiments, the tail wing 512rotates about some other point or a virtual center or the structuresupporting the tail wing 512, rotates with wing 512, or any otherappropriate manner of rotation. In some embodiments, multiple wingsrotate to serve the function of the tail wing 512. In some embodiments,other wings or control surfaces rotate or deflect to modify theaerodynamic characteristics of the kite 501.

In some embodiments, the system is designed such that it maintainsstatic aerodynamic balance at all moments of transition between thecrosswind or static modes of flight and the hover mode of flight. Forexample, a kite which is able to transition between flight modes at anarbitrarily slow rate in high winds. The kite includes surfaces thatengage wind with enough control authority (e.g., a sufficient area on atail control surface that has a moment arm to change the attitude of thekite) to compensate for the time varying forces of buffeting the mainwing (e.g., wind gusts on the wing)

In some embodiments, the system is designed such that the kite mustundergo dynamic maneuvers to transition between flight modes. Forexample, the kite executes a maneuver, where the maneuver once startedneeds to finish. In other words, there is no way to control the kite inthe middle of the maneuvers to stop the maneuver (or restart afterstopping). So, a kite enters the hover mode by pitching up so that itheads straight up slowing down, and when close to stopping in a verticalposition, the kite enters its hovering mode.

FIG. 5C illustrates some of the geometric parameters seen with kite 501when the tail wing 512 is actuated to a position as may be used in hovermode. In this illustrative example, the kite may be facing directlyupward, and the wind may be hitting the kite directly perpendicular tothe bottom of the main wing. In this situation, the lift of the tailwing may be altered to impart a moment around the center of mass, or thecenter of rotation, of the kite. The altering of the lift of the tailwing will result in a change in pitch of the kite, as the change in liftis levered around the distance 550 that the center of lift of the tailwing is rearward (in this configuration) of the center of mass of thekite. The angle 552 of a line drawn through the center of mass of thekite to the center of lift of the tail wing represents the functionalrange that changes in lift may be used to correlate changes in lift ofthe tail wing to a force in the same corresponding direction around thecenter of mass of the kite. Once the kite has pitched backward to thedegree 552 of this line, an increase in lift of the tail wing willresult in a pitch up, whereas until that degree an increase in lift ofthe tail wing will result in a pitch down. The distance 550 that thecenter of lift of the tail wing resides rearward of the center of themass of the kite in this configuration dictates how many degrees off ofvertical the kite may be controlled (using the same force sense) in thehover mode.

FIG. 5D illustrates a variety of pitch conditions 553 of the kite duringhover mode. As seen, the rearward aspect of the tail wing in thisconfiguration (representing a raised aspect during horizontal flight)allows for pitch control utilizing changes in tail wing lift during avariety of possible positions. The rearward aspect of the tail wingallows for sufficient control during a variety of possible conditions,such as wind gusts or other deviations from vertical flight during hovermode.

FIG. 5E illustrates the kite 501 in a partially pitched rearward aspectduring a hover mode operation. Despite the rearward pitch off ofvertical, there is still sufficient angle 551 to allow for good controland pitch stability against wind gusts of the system. In someembodiments, the motor driven propellers of the kite will combine withthe wind to deliver an apparent wind to the tail wing such that evenmore control may be available.

In some embodiments of the present disclosure, as seen in FIG. 6A, thekite 350 is seen in hover mode attached to the bridles 362, which attachto the tether 360. The tail wing 353 is in a horizontal position roughlyperpendicular to the main wing in this configuration. The wind direction361 is seen substantially perpendicular to the main wing. Bridles 362create a torque on the kite 350 when the tether 360 exerts a force whichis not symmetric in kite roll. In such embodiments, the bridles 362restore the roll angle of the kite after disturbances, provided thatsome tether tension is present. By this means, the kite 350 may behovered without sufficient control input to actively maintain a desiredroll, or without any active roll control mechanism or control algorithm.In some embodiments of the present disclosure, bridles such as bridles362 are not present, and tether 360 attaches directly to kite 350. Insome such embodiments, the attachment point is placed to emulate theeffect of bridles 362. In other embodiments, kite 350 may maintain someother means of roll control in hover.

In some embodiments of the present disclosure, the apparent wind of overthe tail wing is a resultant of the actual wind and the propwash overthe tail wing during flight in the hover mode. The tail wing may be useda lifting wing in the apparent wind and effect pitch control asdescribed above.

FIG. 6B shows another view of the kite 350 in hover mode attached to thebridles 362. In some embodiments, the bridles 362 may include two ormore bridles that are adapted to provide a torque (or a moment) on thekite 350 to control a roll of the kite 350. For instance, in theillustrated example, the bridles 362 include two bridles, a first bridle362A and a second bridle 362B. However, in other examples, the bridles362 may include more than two bridles, such as three bridles, fourbridles, etc. In addition, in some embodiments, the bridles 362 may eachhave a length of 4 to 5 meters. Other lengths of the bridles 362 arepossible as well. In some embodiments, the torque may be a cross productof a force vector and a distance vector.

As shown in FIG. 6B, the first bridle 362A is attached to a first side352A of a main wing 352 and the second bridle is attached to a secondside 352B of the main wing 352. The first side 352A of the main wing 352is opposite of the second side 352B of the main wing 352. In someembodiments, the first bridle 362A may be oriented substantiallyparallel to the second bridle 362B. For instance, the first bridle 362Amay be oriented parallel to the second bridle 362B or a deviation fromparallel that does not cause the kite 350 to operate in a significantlydifferent manner from when the first bridle 362A is oriented parallel tothe second bridle 362B. Moreover, in some embodiments, the first bridle362A may be oriented at an angle to the second bridle 362B. In suchembodiments, the angle may be from an axis defined by the main wing 352.

Further, in some embodiments, in response to a force on the kite 350provided by the tether 360, the first bridle 362A and the second bridle362B may be adapted to provide the torque on the kite 350 to control theroll of the kite 350, such that the torque causes a change in the rollof the kite. And in at least one such embodiment, the force on the kite350 may be asymmetric along a roll axis 370. In some examples, the rollaxis 370 may take the form of or be similar in form to the axis 517.

In some examples, other components of the kite 350 may be adapted toprovide a second torque (or a second moment) on the kite 350 thatopposes the torque provided by the first bridle 362A and the secondbridle 362B. For instance, in some embodiments, the rotors 351 mountedto the main wing 352 using the pylons 356 may be adapted to provide asecond torque on the kite 350 and in response to a force on the kiteprovided by the tether 360 and the second torque on the kite 350, thefirst bridle 362A and the second bridle 362B may be adapted to providethe torque on the kite 350, such that the torque on the kite causes achange in the roll of the kite 350. And in at least one such embodiment,the second torque on the kite 350 provided by the rotors 351 may besubstantially opposite the torque on the kite 350 along the roll axis370 provided by the first bridle 362A and the second bridle 362B. Forinstance, the second torque may be opposite the torque or a deviationfrom opposite that does not cause the kite 350 to operate in asignificantly different manner from when the second torque is oppositethe torque. In some embodiments, the second torque may be a crossproduct of a force vector and a distance vector. The rotors 351 may takethe form of or be similar in form to the rotors 310.

In the illustrated example, the rotors 351 include four rotors. In someembodiments, when the rotors 351 are adapted to provide the secondtorque on the kite 350, each of the rotors 351 may rotate insubstantially the same direction. For instance, when the rotors 351 areproviding thrust each of the rotors 351 may rotate in the same directionor a deviation from the same that does not cause the kite 350 to operatein a significantly different manner. Moreover, in some embodiments, whenthe rotors 351 are adapted to provide the second torque on the kite 350,some or all of the rotors 351 may rotate in different directions.Further, in some embodiments, when the rotors 351 are providing thrusteach of the rotors 351 may rotate with substantially the same speed. Forinstance, each of the rotors may rotate with the same speed or adeviation from the same that does not cause the kite 350 to operate in asignificantly different manner. Moreover, in some embodiments, when therotors 351 are adapted to provide the second torque on the kite 350,some or all of the rotors may rotate with different speeds.

In some examples, other components of the kite 350 may be adapted toprovide a second torque on the kite 350, such that the torque on thekite 350 provided by the first bridle 362A and the second bridle 362Band the second torque on the kite 350 cause a change in the roll of thekite 350. With this arrangement, the second torque may augment thetorque. For instance, in some embodiments, the rotors 351 may be adaptedto provide a second torque on the kite 350 and in response to a force onthe kite 350 provided by the tether 360, the first bridle 362A and thesecond bridle 362B may be adapted to provide the torque on the kite 350,such that the torque on the kite 350 and the second torque on the kite350 cause a change in the roll of the kite 350. And in at least one suchembodiment, the second torque on the kite 350 provided by the rotors 351may be substantially parallel to the torque on the kite 350 along theroll axis 370 provided by the first bridle 362A and the second bridle362B. For instance, the second torque may be parallel to the torque or adeviation from parallel that does not cause the kite 350 to operate in asignificantly different manner from when the second torque is parallelto the torque.

Further, in at least one such embodiment, the torque on the kite 350provided by the first bridle 362A and the second bridle 362B may have amagnitude that is greater than a magnitude of the second torque on thekite 350 provided by the rotors 351. However, in other embodiments, thetorque on the kite 350 may have a magnitude that is less than amagnitude of the second torque on the kite 350. For instance, in someembodiments, when the magnitudes of the torque and the second torque arecombined, the torque may be 90 to 95 percent of the combination of thetorque and the second torque.

The magnitude of the torque on the kite 350 provided by the first bridle362A and the second bridle 362B may depend on wind speed and tension inthe tether 360. In some embodiments, as the wind speed and the tensionin the tether 360 increase, the magnitude of the torque provided by thefirst bridle 362A and the second bridle 362B may increase. In someexamples, when the wind speed is low and the tension in the tether 360is low, the magnitude of the torque provided by the first bridle 362Aand the second bridle 362B may be less than the magnitude of the secondtorque provided by the rotors 351. Moreover, in some examples, when thewind speed is high and the tension in the tether 360 is high, themagnitude of the torque provided by the first bridle 362A and the secondbridle 362B may be greater than the second torque provided by the rotors351.

In some examples, the magnitude of the torque on the kite 350 providedby the first bridle 362A and the second bridle 362B may be between 10Kilonewton-meter per radian (kN-m/rad) and 130000 kN-m/rad and eachrotor of the rotors 351 may provide a torque with a magnitude of 400Newton-meters (Nm). With this arrangement, the magnitude of the secondtorque on the kite 350 provided by the rotors 351 may be N multiplied by400 Nm, where N is the number of rotors.

In some examples, when the magnitude of the torque on the kite 350provided by the first bridle 362A and the second bridle 362B is lessthan the magnitude of the second torque provided by the rotors 351(e.g., when the magnitude of the torque is 10 kN-m/rad), the secondtorque on the kite 350 provided by the rotors 351 may contribute more tocausing a change in the roll of the kite 350 than the torque on the kite350 provided by the first bridle 362A and the second bridle 362B. And insuch examples, the second torque on the kite 350 provided by the rotors351 may assist with stabilizing the kite 350.

Moreover, in some examples, when the magnitude of the torque on the kite350 provided by the first bridle 362A and the second bridle 362B isgreater than the magnitude of the second torque on the kite 350 providedby the rotors 351 (e.g., when the magnitude of the torque is 130000kN-m/rad), the second torque on the kite 350 provided by the rotors 351may contribute less to causing a change in the roll of the kite 350 thanthe torque on the kite 350 provided by the first bridle 362A and thesecond bridle 362B.

Moreover, in some embodiments, the main wing 352 may include one or morecontrol surfaces 315 that are adapted to provide a second torque on thekite 350 and in response to a force on the kite 350 provided by thetether 360, the first bridle 362A and the second bridle 362B may beadapted to provide the torque on the kite, such that the torque on thekite 350 and the second torque on the kite 350 cause a change in theroll of the kite. And in at least in one such embodiment, the secondtorque on the kite 350 provided by the one or more control surfaces 315may be substantially parallel to the torque on the kite 350 along theroll axis 370 provided by the first bridle 362A and the second bridle362B. For instance, the second torque may be parallel to the torque or adeviation from parallel that does not cause the kite 350 to operate in asignificantly different manner from when the second torque is parallelto the torque.

Further, in at least one such embodiment, the torque on the kite 350provided by the first bridle 362A and the second bridle 362B may have amagnitude that is greater than a magnitude of the second torque on thekite provided by the one or more control surfaces 315. However, in otherembodiments, the torque on the kite 350 may have a magnitude that isless than a magnitude of the second torque on the kite 350.

The one or more control surfaces 315 may take various different forms invarious different embodiments. For instance, the one or more controlsurfaces 315 may include winglets, flaps (e.g., Fowler flaps, Hoernerflaps, split flaps, and the like), rudders, elevators, spoiler, divebrakes, etc. Further, the one or more control surfaces 315 may belocated on a leading edge of the main 352 and/or a trailing edge of themain wing 352.

Moreover, in some embodiments, the main wing 352 may be curved, suchthat the main wing 352 is adapted to provide a second torque on the kite350 and in response to a force on the kite provided by the tether 360,the first bridle 362A and the second bridle 362B may be adapted toprovide the torque on the kite 350, such that the torque on the kite 350and the second torque on the kite 350 cause a change in the roll of thekite 350. And in at least in one such embodiment, the second torque onthe kite 350 provided by the main wing 352 may be substantially parallelto the torque on the kite 350 along the roll axis 370 provided by thefirst bridle 362A and the second bridle 362B. For instance, the secondtorque may be parallel to the torque or a deviation from parallel thatdoes not cause the kite 350 to operate in a significantly differentmanner from when the second torque is parallel to the torque. In otherembodiments, the main wing 352 may be substantially flat. For instance,the main wing 352 may be flat or a deviation from flat that does notcause the kite 350 to operate in a significantly different manner fromwhen the main wing 352 is flat.

The curvature of the main wing 352 may take various different forms invarious different embodiments. For instance, the main wing 352 may havea dihedral, such that the main wing 352 is adapted to provide a secondtorque on the kite 350. As another example, the main wing 352 may have apolyhedral angle, such that the main wing 352 is adapted to provide asecond torque on the kite 350. In some embodiments, the polyhedral anglemay be between 5 to 10 degrees starting at a semispan of the main wing352. Moreover, in some embodiments, the polyhedral angle may be 20degrees for a span of the main wing 352, such as 0.1 of the span from anedge of the main wing 352. Further, in some embodiments, the main wing352 may follow an arc or a parabolic polyhedral distribution.

Further, in at least one such embodiment, the torque on the kite 350provided by the first bridle 362A and the second bridle 362B may have amagnitude that is greater than a magnitude of the second torque on thekite provided by the main wing 352. However, in other embodiments, thetorque on the kite 350 may have a magnitude that is less than amagnitude of the second torque on the kite 350.

Although the bridles 362 have been described above as being adapted toprovide a torque to control a roll of the kite 350 when the kite 350 isin the hover mode of flight, in other examples the bridles 362 may beadapted to provide a torque to control a roll of the kite 350 when thekite 350 is in the crosswind mode of flight.

Similarly, although other components of the kite 350 (e.g., the rotors351) have been described above as being adapted to provide a secondtorque on the kite 350 that opposes the torque provided by the firstbridle 362A and the second bridle 362B when the kite 350 is in the hovermode of flight, in other examples the other components may be adapted toprovide a second torque on the kite that opposes the torque provided bythe first bridle 362A and the second bridle 362B when the kite 350 is inthe crosswind mode of flight. Further, although other components of thekite 350 (e.g., the rotors 351 and/or the main wing 352) have beendescribed above as being adapted to provide a second torque on the kite350, such that the torque on the kite 350 and the second torque on thekite 350 cause a change in the roll of the kite 350 when the kite 350 inthe hover mode of flight, in other examples the other components of thekite 350 may be adapted to provide a second torque on the kite 350, suchthat the torque on the kite 350 and the second torque on the kite 350cause a change in the roll of the kite 350 when the kite 350 is in thecrosswind mode of flight. In some examples, the rotors 351 may beadapted to provide the second torque on the kite 350 when the rotors 351generate electrical energy while in the crosswind flight mode.

In some embodiments of the present disclosure, as seen in FIG. 7, thekite 501 is seen mounted to a support structure 701 adapted to receivethe kite 501 during a landing, and to support the kite 501 prior to takeoff. In some embodiments, a winch 702 may be adapted to reel in thetether 502 during landing of the kite 501. The support structure 701 mayreside on the ground 703 in some aspects, or in other locations.

Further, in some examples, illustrative bridles may be adapted toprovide a torque to control a roll of a kite when a kite is lifting offor landing in the hover mode of flight. FIG. 8 shows a view of a kite850 attached to bridles 862. The bridles 862 attach to the tether 860.In the illustrated example, a winch 802 may be adapted to deploy thetether 860 during lift off and reel in the tether 860 during landing. Insome embodiments, a ground-side gimble 804 may be adapted to unwind thetether 860 during lift off.

The kite 850 may be similar in form to the kite 350. For instance, asshown in FIG. 8, the kite 850 includes a main 852 and rotors 851 thatmay be mounted to the main wing 852 using pylons 856. In the illustratedexample, the rotors 851 includes eight rotors: a first rotor 851A, asecond rotor 851B, a third rotor 851C, a fourth rotor 851D, a fifthrotor 851E, a sixth rotor 851F, a seventh rotor 851G, and an eighthrotor 851H. Some of or all of the rotors 851 may take the form of or besimilar in form to the rotors 351. In addition, the main wing 852 maytake the form of or be similar in form to the main wing 352. Forinstance, in some embodiments, the main wing 852 may include one or morecontrol surfaces. Moreover, in some embodiments, the main wing 852 maybe curved or substantially flat. Further still, the pylons 856 may takethe form of or be similar in form to the pylons 356.

The bridles 862 may be similar in form to the bridles 362. In theillustrated example, the bridles 862 includes three bridles: a firstbridle 862A, a second bridle 862B, and a third bridle 862C. The firstbridle 862A, the second bridle 862B, and/or the third bridle 862C may beattached to the main wing 852 in the same or similar way as the firstbridle 362A and/or the second bridle 362B may be attached to the mainwing 352. In addition, the first bridle 862A, the second bridle 862B,and/or the third bridle 862C may be oriented in the same or similar wayas the first bridle 362A and/or the second bridle 362B may be oriented.For instance, as shown in FIG. 8, the main wing 852 may include a firstside 852A, a second side 852B, and a center line 852C, and the firstbridle 862A may be attached to the first side 852A of the main wing 852,the third bridle 862C may be attached to the second side 852B of themain wing 852, and the second bridle 862B may be attached to a portionon the main wing 852 that is located substantially on the center line852C. For instance, the portion may be on the centerline 852C or adeviation from on the centerline 852C that does not cause the kite 850to operate in a significantly different manner from when the portion ison the centerline 852C.

The first bridle 862A, the second bridle 862B, and the third bridle 862Cmay be adapted to provide a torque to control a roll of the kite 850when the kite 850 is lifting off and/or landing in the same or similarway as the first bridle 362A and the second bridle 362B may be adaptedto provide a torque to control a roll of the kite 350 as described withreference to FIGS. 6A and 6B. In some embodiments, control of the rollof the kite 850 may allow the kite 850 to contact a perch (not shown)associated with the winch 802.

Moreover, the rotors 851 may be adapted to provide a second torque onthe kite 850 that opposes the torque provided by the first bridle 862A,the second bridle 862B, and the third bridle 862C when the kite 850 islifting off and/or landing in the same or similar way as the rotors 351may be adapted to provide a second torque on the kite 350 that opposesthe torque provided by the first bridle 362A and the second bridle 362B.For instance, in some embodiments, each of the rotors 851 may rotate insubstantially the same direction and/or substantially the same speed. Inaddition, in some embodiments, the first rotor 851A, the second rotor851B, the third rotor 851C, and the fourth rotor 851D may rotate in afirst direction; and the fifth rotor 851E, the sixth rotor 851F, theseventh rotor 851G, and the eighth rotor 851H may rotate in a seconddirection. And in at least one such embodiment, the first direction maybe substantially opposite the second direction. For instance, the firstdirection may be opposite the second direction or a deviation fromopposite that does not cause the kite 850 to operate in a significantlydifferent manner when the first direction is opposite the seconddirection.

Further, the rotors 851 may be adapted to provide a second torque on thekite 850, such that the torque on the kite 850 and the second torque onthe kite 850 cause a change in the roll of the kite when the kite 850 islifting off and/or landing in the same or similar way as the rotors 351may be adapted to provide a second torque on the kite 350, such that thetorque on the kite 350 and the second torque on the kite 350 cause achange in the roll of the kite as described with reference to FIG. 6B.For instance, the second torque may be substantially opposite the torquealong a roll axis 870. The roll axis 870 may take the form of or besimilar in form to the roll axis 370. In FIG. 8, the roll axis 870 maybe directed out of the page (as indicated by the counterclockwisearrow).

Further, the main wing 852 may be adapted to provide a second torque onthe kite 850, such that the torque on the kite 850 and the second torqueon the kite 850 cause a change in the roll of the kite when the kite 850is lifting off and/or landing in the same or similar way as the mainwing 352 may be adapted to provide a second torque on the kite 350, suchthat the torque on the kite 350 and the second torque on the kite 350cause a change in the roll of the kite as described with reference toFIG. 6B. For instance, the second torque may be substantially parallelto the torque along the roll axis 870.

In some examples, when the kite 850 lands, the kite 850 may bepositioned at a roll angle, a yaw angle, and pitch angle. In someembodiments, the roll angle may be 5 degrees, the yaw angle may be 7degrees, and the pitch angle may 10 degrees.

FIG. 9 is a flow chart illustrating a method 900, according to anexample embodiment. The method 900 may include one or more operations,functions, or actions as illustrated by one or more blocks 902-904.Although the blocks are illustrated in a sequential order, these blocksmay in some instances be performed in parallel. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or removed based upon the desired implementation.

Illustrative methods, such as method 900, may be carried out in whole orin part by a component or components of a kite. For simplicity, method900 may be described generally as being carried out by a kite, such asthe kite 350 and the kite 850. However, it should be understood thatexample methods, such as method 900, may be carried out by otherentities or combinations of entities without departing from the scope ofthis disclosure.

At block 902, the method 900 involves causing a kite to lift off theground in a hover mode of flight. The kite may include a main wing. Andthe kite may be oriented vertically in the hover mode of flight. Thekite may take the form of or be similar in form to the kite 101, thekite 201, the kite 350, the kite 401, the kite 501 and/or the kite 850,and the main wing may take the form of or be similar in form to the mainwing 311, the main wing 352, the main wing 511, and/or the main wing852.

At block 904, the method 900 involves controlling a roll of the kiteduring the hover mode of flight at least in part with use of two or morebridles between the kite and a tether. Each bridle of the two or morebridles may be attached to the main wing, and the two or more bridlesmay be adapted to provide a torque on the kite to control the roll ofthe kite. The two or more bridles may take the form of or be similar inform to the first bridle 362A and the second bridle 362B and/or thefirst bridle 862A, the second bridle 862B, and the third bridle 862C.

In some embodiments, in response to a force on the kite provided by thetether, the two or more bridles may be adapted to provide the torque onthe kite to control the roll of the kite, such that the torque on thekite causes a change in the roll of the kite. Moreover, in someembodiments, causing the kite to lift off the ground in the hover modeof flight may involve controlling the roll of the kite during lift offat least in part with the use of the two or more bridles. Further, insome embodiments, the kite may further include one or more rotorsattached to the main wing, wherein the one or more rotors may be adaptedto provide a second torque on the kite that is substantially oppositethe torque on the kite along a roll axis of the kite, and wherein inresponse to (i) a force on the kite provided by the tether and (ii) thesecond torque on the kite, the two or more bridles may be adapted toprovide the torque on the kite, such that the torque on the kite causesa change in the roll of the kite. Further still, in some embodiments,the kite may further include one or more rotors attached to the mainwing, wherein the one or more rotors may be adapted to provide a secondtorque on the kite that is substantially parallel to the torque on thekite along a roll axis of the kite, and wherein in response to a forceon the kite provided by the tether, the two or more bridles may beadapted to provide the torque on the kite, such that the torque on thekite and the second torque on the kite cause a change in the roll of thekite. The one or more rotors may take the form of or be similar in formto the rotors 310, the rotors 351, and/or the rotors 851.

Moreover, in some embodiments, the main wing may include one or morecontrol surfaces, and wherein the one or more control surfaces areadapted to provide a second torque that is substantially parallel to thetorque on the kite along a roll axis of the kite, and wherein inresponse to a force on the kite provided by the tether, the two or morebridles are adapted to provide the torque on the kite, such that thetorque on the kite and the second torque on the kite cause a change inthe roll of the kite. Further, in some embodiments, the main wing may becurved, such that the main wing is adapted to provide a second torquethat is substantially parallel to the torque on the kite along a rollaxis of the kite, and wherein in response to a force on the kiteprovided by the tether, the two or more bridles may be adapted toprovide the torque on the kite, such that the torque on the kite and thesecond torque on the kite cause a change in the roll of the kite.

Further, the method 900 may further involve landing the kite in thehover mode of flight. The landing may involve controlling the roll ofthe kite at least in part with the use of the two or more bridles.

FIG. 10 is a flow chart illustrating a method 1000, according to anexample embodiment. The method 1000 may include one or more operations,functions, or actions as illustrated by one or more blocks 1002-1006.Although the blocks are illustrated in a sequential order, these blocksmay in some instances be performed in parallel. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or removed based upon the desired implementation.

Illustrative methods, such as method 1000, may be carried out in wholeor in part by a component or components of a kite. For simplicity,method 1000 may be described generally as being carried out by a kite,such as the kite 350 and the kite 850. However, it should be understoodthat example methods, such as method 1000, may be carried out by otherentities or combinations of entities without departing from the scope ofthis disclosure.

At block 1002, the method 1000 involves causing a kite to lift off theground in a hover mode of flight. The kite may include a main wing. Andthe kite may be oriented vertically in the hover mode of flight. Thekite may take the form of or be similar in form to the kite 101, thekite 201, the kite 350, the kite 401, the kite 501 and/or the kite 850,and the main wing may take the form of or be similar in form to the mainwing 311, the main wing 352, the main wing 511, and/or the main wing852.

At block 1004, the method 1000 involves transitioning the kite from thehover mode of flight to a crosswind mode of flight. The kite may beoriented horizontally in the crosswind mode of flight. In someembodiments, the kite may transition from the hover mode of flight tothe crosswind mode of flight via forward flight and/or a flight maneuver(e.g., pitching forward).

At block 1006, the method 1000 involves controlling a roll of the kiteduring the crosswind mode of flight at least in part with use of two ormore bridles between the kite and a tether. Each bridle of the two ormore bridles may be attached to the main wing, and the two or morebridles may be adapted to provide a torque on the kite to control theroll of the kite. The two or more bridles may take the form of or besimilar in form to the first bridle 362A and the second bridle 362Band/or the first bridle 862A, the second bridle 862B, and the thirdbridle 862C.

In some embodiments, in response to a force on the kite provided by thetether, the two or more bridles may be adapted to provide the torque onthe kite to control the roll of the kite, such that the torque on thekite causes a change in the roll of the kite. Moreover, in someembodiments, causing the kite to lift off the ground in the hover modeof flight may involve controlling the roll of the kite during lift offat least in part with the use of the two or more bridles. Further, insome embodiments, the kite may further include one or more rotorsattached to the main wing, wherein the one or more rotors may be adaptedto provide a second torque on the kite that is substantially oppositethe torque on the kite along a roll axis of the kite, and wherein inresponse to (i) a force on the kite provided by the tether and (ii) thesecond torque on the kite, the two or more bridles may be adapted toprovide the torque on the kite, such that the torque on the kite causesa change in the roll of the kite. Further still, in some embodiments,the kite may further include one or more rotors attached to the mainwing, wherein the one or more rotors may be adapted to provide a secondtorque on the kite that is substantially parallel to the torque on thekite along a roll axis of the kite, and wherein in response to a forceon the kite provided by the tether, the two or more bridles may beadapted to provide the torque on the kite, such that the kite and thesecond torque on the kite cause a change in the roll of the kite. Theone or more rotors may take the form of or be similar in form to therotors 310, the rotors 351, and/or the rotors 851.

Moreover, in some embodiments, the main wing may include one or morecontrol surfaces, and wherein the one or more control surfaces areadapted to provide a second torque that is substantially parallel to thetorque on the kite along a roll axis of the kite, and wherein inresponse to a force on the kite provided by the tether, the two or morebridles are adapted to provide the torque on the kite, such that thetorque on the kite and the second torque on the kite cause a change inthe roll of the kite. Further, in some embodiments, the main wing may becurved, such that the main wing is adapted to provide a second torquethat is substantially parallel to the torque on the kite along a rollaxis of the kite, and wherein in response to a force on the kiteprovided by the tether, the two or more bridles may be adapted toprovide the torque on the kite, such that the torque on the kite and thesecond torque on the kite cause a change in the roll of the kite.

Further, method 1000 may further involve controlling a roll of the kiteduring the hover mode of flight at least in part with the use of the twoor more bridles. Further still, method 1000 may further involve landingthe kite in the hover mode of flight, wherein the landing may involvecontrolling the roll of the kite at least in part with the use of thetwo or more bridles.

While various aspects of the disclosure have been disclosed herein,other aspects and embodiments will be apparent to those skilled in theart. Accordingly, the embodiments disclosed herein are for purposes ofillustration, and are not intended to be limiting, with the true scopeof the disclosure being indicated by the following claims.

What is claimed is:
 1. A system comprising: a ground station; a tetherattached to the ground station on a first end and to two or more bridleson a second end; and a kite comprising: a main wing, wherein each bridleof the two or more bridles is attached to the main wing, and wherein thetwo or more bridles are adapted to provide a torque on the kite tocontrol a roll of the kite.
 2. The system of claim 1, wherein the kitefurther comprises a tail wing rearward and above the main wing.
 3. Thesystem of claim 1, wherein the two or more bridles comprise: a firstbridle attached to a first side of the main wing, and a second bridleattached to a second side of the main wing opposite the first side ofthe main wing.
 4. The system of claim 3, wherein the first bridle isoriented substantially parallel to the second bridle.
 5. The system ofclaim 3, wherein the first bridle is oriented at an angle to the secondbridle.
 6. The system of claim 1, wherein the main wing comprises acenter line, and wherein the two or more bridles comprise: a firstbridle attached to a first side of the main wing, a second bridleattached to a second side of the main wing opposite the first side ofthe main wing, and a third bridle attached to a portion of the mainwing, wherein the portion is located substantially on the center line ofthe main wing.
 7. The system of claim 1, wherein in response to a forceon the kite provided by the tether, the two or more bridles are adaptedto provide the torque on the kite to control the roll of the kite, suchthat the torque causes a change in the roll of the kite.
 8. The systemof claim 7, wherein the force on the kite is asymmetric along a rollaxis of the kite.
 9. The system of claim 1, wherein the kite furthercomprises one or more rotors attached to the main wing, wherein the oneor more rotors are adapted to provide a second torque on the kite thatis substantially opposite the torque on the kite along a roll axis ofthe kite, and wherein in response to (i) a force on the kite provided bythe tether and (ii) the second torque on the kite, the two or morebridles are adapted to provide the torque on the kite, such that thetorque on the kite causes a change in the roll of the kite.
 10. Thesystem of claim 9, wherein each rotor of the one or more rotors rotatesin substantially the same direction.
 11. The system of claim 1, whereinthe kite further comprises one or more rotors attached to the main wing,wherein the one or more rotors are adapted to provide a second torque onthe kite that is substantially parallel to the torque on the kite alonga roll axis of the kite, and wherein in response to a force on the kiteprovided by the tether, the two or more bridles are adapted to providethe torque on the kite, such that the torque on the kite and the secondtorque on the kite cause a change in the roll of the kite.
 12. Thesystem of claim 11, wherein the torque on the kite has a magnitude thatis greater than a magnitude of the second torque on the kite.
 13. Thesystem of claim 1, wherein the main wing comprises one or more controlsurfaces, and wherein the one or more control surfaces are adapted toprovide a second torque that is substantially parallel to the torque onthe kite along a roll axis of the kite, and wherein in response to aforce on the kite provided by the tether, the two or more bridles areadapted to provide the torque on the kite, such that the torque on thekite and the second torque on the kite cause a change in the roll of thekite.
 14. The system of claim 1, wherein the main wing is curved, suchthat the main wing is adapted to provide a second torque that issubstantially parallel to the torque on the kite along a roll axis ofthe kite, and wherein in response to a force on the kite provided by thetether, the two or more bridles are adapted to provide the torque on thekite, such that the torque on the kite and the second torque on the kitecause a change in the roll of the kite.
 15. A method comprising: causinga kite to lift off the ground in a hover mode of flight, wherein thekite comprises a main wing, wherein the kite is oriented vertically inthe hover mode of flight; and controlling a roll of the kite during thehover mode of flight at least in part with use of two or more bridlesbetween the kite and a tether, wherein each bridle of the two or morebridles is attached to the main wing, and wherein the two or morebridles are adapted to provide a torque on the kite to control the rollof the kite.
 16. The method of claim 15, wherein in response to a forceon the kite provided by the tether, the two or more bridles are adaptedto provide the torque on the kite to control the roll of the kite, suchthat the torque on the kite causes a change in the roll of the kite. 17.The method of claim 15, wherein causing the kite to lift off the groundin the hover mode of flight comprises controlling the roll of the kiteduring the lift off at least in part with the use of the two or morebridles.
 18. The method of claim 15, wherein the kite further comprisesone or more rotors attached to the main wing, wherein the one or moremotors are adapted to provide a second torque on the kite that issubstantially parallel to the torque on the kite along a roll axis ofthe kite, and wherein in response to a force on the kite provided by thetether, the two or more bridles are adapted to provide the torque on thekite, such that torque on the kite and the second torque on the kitecause a change in the roll of the kite.
 19. The method of claim 15,wherein the method further comprises: landing the kite in the hover modeof flight, wherein the landing comprises controlling the roll of thekite at least in part with the use of the two or more bridles.
 20. Amethod comprising: causing a kite to lift off the ground in a hover modeof flight, wherein the kite comprises a main wing, wherein the kite isoriented vertically in the hover mode of flight; transitioning the kitefrom the hover mode of flight to a crosswind mode of flight, wherein thekite is oriented horizontally in the crosswind mode of flight; andcontrolling a roll of the kite during the crosswind mode of flight atleast in part with use of two or more bridles between the kite and atether, wherein each bridle of the two or more bridles is attached tothe main wing, and wherein the two or more bridles are adapted toprovide a torque on the kite to control the roll of the kite.